Virtual image formation method for an ultrasound device

ABSTRACT

Disclosed are ultrasound devices and methods for use in guiding a subdermal probe during a medical procedure. A device can be utilized to guide a probe through the probe guide to a subdermal site. In addition, a device can include a detector in communication with a processor. The detector can recognize the location of a target associated with the probe. The processor can utilize the data from the detector and create an image of a virtual probe that can accurately portray the location of the actual probe on a sonogram of a subdermal area. In addition, disclosed systems can include a set of correlation factors in the processor instructions. As such, the virtual probe image can be correlated with the location of the actual probe.

BACKGROUND OF THE INVENTION

Medical probe devices are utilized for many purposes, chief of whichinclude catheterization, centesis, and biopsy procedures. Percutaneousplacement of probes using these devices is often performed withtechniques which rely on ascertaining the correct locations of palpableor visible structures. This is neither a simple nor a risk-freeprocedure. For instance, proper insertion and placement of a subdermalprobe depends on correct localization of anatomical landmarks, properpositioning of the patient in relation to the care provider, andawareness of both the depth of the subdermal location and angle from thepoint of probe insertion. Risks of unsuccessful placement of a probe canrange from minor complications, such as patient anxiety and discomfortdue to repetition of the procedure following incorrect initialplacement, to severe complications, such as pneumothorax, arterial orvenous laceration, or delay of delivery of life-saving fluids ormedications in an emergency situation.

Ultrasound guided techniques and devices have been developed to aid incorrect placement of percutaneous probes. Ultrasound guided techniquesoften utilize two people, an ultrasound operator who locates theinternal site and keeps an image of the site centrally located on amonitor, and a care provider who attempts to guide the probe to the sitebased upon the sonogram. Such techniques are very difficultperceptually. For instance, these techniques are complicated by the factthat the person guiding the probe to the internal site is not the sameperson as is operating the ultrasound. In addition, the generally thin,cylindrical probe is usually small and reflects very little of theultrasound beam. Moreover, as the cylindrical probe and the ultrasoundbeam are not generally normal to one another, the small amount ofultrasonic energy that is reflected from the probe will reflect at anangle to the incident beam, resulting in little if any of the reflectedenergy being detected by the ultrasound transducer. As a result, theprobe itself is difficult to visualize in the sonogram and the personplacing the probe must attempt to guide the probe to the correctlocation using minimal visual feedback. For example, the only visualfeedback available is often only subtle artifacts of the motion of theprobe such as slight changes in the sonogram as the probe deflects andpenetrates the surrounding tissue. The trained observer can pick upsubtle ultrasonic shadow artifacts deep to the probe created when theprobe blocks the transmission of the ultrasound beam to the tissuebelow, and such subtle artifacts can be used to help guide the probe tothe desired subdermal location.

In an attempt to relieve the difficulties of ultrasound guided probetechniques, systems have been developed including a probe guide whichcan be attached to an ultrasound transducer housing. Problems stillexist with such devices however. For instance, the probe is ofteninserted at angle that crosses the scanned plane displayed on thesonogram, restricting the intersection of the scanned plane and thepoint of the probe to a very small area in space. In addition, even ifthe probe passes for a length in line with the scanned plane, verylittle, if any, ultrasonic energy is reflected from the probe back tothe transducer. In fact, due to the lack of reflection off of the probe,visual cues to the location of the probe tip may be even more difficultto discern on a sonogram when using these devices. In addition, in manyof these devices, the probe passes through the ultrasound beam at afixed depth range depending on the set angle of the probe guide, andthis may not correspond to the depth of the desired subdermal site, inwhich case it may not be possible to show the juncture of the desiredsite and the probe tip on the sonogram at all.

What are needed in the art are improved ultrasound devices and methodsfor using such devices. For instance, what are needed in the art areultrasound devices that can be utilized by a single operator toaccurately visualize the delivery of a probe to a subdermal location.

SUMMARY OF THE INVENTION

According to one embodiment, disclosed is a method for guiding a probetip to a subdermal site. For instance, a method can include guiding aprobe through a probe guide of an ultrasound device. The ultrasounddevice can include an ultrasound transducer and a detector, both incommunication with a processor. The detector can determine the locationof a target that is associated with the probe.

A method can also include configuring the processor to determine thelocation of a virtual probe tip from the location of the target asdetermined by the detector and communicated to the processor.Specifically, the processor can execute instructions provided viasoftware to determine the location of the virtual probe tip. Theinstructions can include a set of correlation factors that correlate thelocation of the virtual probe tip as determined by the processor withthe subdermal location of the probe tip.

A method can also include forming a sonogram of the subdermal site on amonitor from information communicated to the processor from theultrasound transducer, and forming an image on the sonogram of thelocation of the virtual probe tip as determined and correlated by theprocessor from information communicated to the processor from thedetector.

A method can also include configuring the processor to determine when aprobe has been flexed such that it is out of alignment with the probeguide. For instance, the processor software can determine an index levelthat can indicate movement of the target away from the detector.Moreover, the processor can trigger an alarm when the index levelexceeds a predetermined value, indicating that the target associatedwith the probe has been moved too far from the detector.

Also disclosed herein is an ultrasound device that can include anultrasound transducer, a detector, and a processor. For instance, thedetector can include an array of sensors. In one preferred embodiment,the sensors can be Hall effect transducers and the target that isassociated with the probe for use with the device can be a magnet.

An ultrasound device can include additional components as well. Forexample, a device can include an alarm that can be triggered when aprobe is flexed out of alignment with the probe guide (e.g., the indexlevel determined by the processor exceeds a predetermined value). Anultrasound device can also include features such as one or more of asterilizable shield that encloses at least a portion of the ultrasounddevice, and a clamp for clamping a probe within the probe guide.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present subject matter, includingthe best mode thereof to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures in which:

FIG. 1A illustrates an ultrasound device including a series of Halleffect sensors along a length of the ultrasound device.

FIGS. 1B and 1C illustrate two embodiments of arrays of Hall effectsensors as may be utilized in disclosed ultrasound devices.

FIG. 2 illustrates the ultrasound device of FIG. 1A upon deformation ofa probe during use.

FIG. 3A illustrates an overlay of a FIGS. 1 and 2.

FIG. 3B illustrates a portion of FIG. 3A.

FIGS. 4A and 4B graphically illustrate the change in the magnetic fieldstrength along a sensor array for an aligned probe (FIG. 4A) and a probethat is flexed out of alignment (FIG. 4B)

FIG. 5A illustrates an ultrasound device including a series of sensorson the base of the ultrasound device.

FIG. 5B illustrates a top view of the ultrasound device of FIG. 5A.

FIG. 5C illustrates a top view of another embodiment of an array ofsensors on the base of an ultrasound device.

FIG. 6 illustrates the ultrasound device of FIG. 5A upon deformation ofa probe during use.

FIG. 7 illustrates a sterilizable shield that can encase an ultrasounddevice.

FIG. 8 illustrates the bottom portion of the sterilizable shield of FIG.7.

FIG. 9 illustrates the top portion of a sterilizable shield, the bottomportion of which is illustrated in FIG. 8.

FIG. 10 illustrates another embodiment of an ultrasound device asdisclosed herein.

FIG. 11 illustrates a partially exploded version of the ultrasounddevice as is illustrated in FIG. 10.

FIG. 12 illustrates another embodiment of an ultrasound device asdisclosed herein.

FIG. 13 illustrates a system as utilized in the Example, providedherein.

FIG. 14 illustrates a geometric description of a magnet tilt calculationmodel, as described herein.

FIG. 15 graphically illustrates the shift in sensor readings upon flexin a probe as a function of the tilt of a target magnet.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features ofelements of the disclosed subject matter. Other objects, features andaspects of the subject matter are disclosed in or are obvious from thefollowing detailed description.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to various embodiments of thedisclosed subject matter, one or more examples of which are set forthbelow. Each embodiment is provided by way of explanation of the subjectmatter, not limitation of the subject matter. In fact, it will beapparent to those skilled in the art that various modifications andvariations may be made in the present disclosure without departing fromthe scope or spirit of the subject matter. For instance, featuresillustrated or described as part of one embodiment, may be used inanother embodiment to yield a still further embodiment. Thus, it isintended that the present disclosure cover such modifications andvariations as come within the scope of the appended claims and theirequivalents.

Definitions

As utilized herein, the term “probe” generally refers to an item thatcan be guided to a subdermal location, for instance for delivery of atherapeutic, e.g., a compound or a treatment, to the location; forremoval of material from the location; and so forth. For example, theterm “probe” can refer to a needle, a tube, a biopsy needle or blade, orany other item that can be guided to a subdermal location. In general, aprobe can be guided by and used in conjunction with an ultrasound deviceas described herein. A probe can define a ratio of the length of theprobe to the diameter (or a width) of the probe greater than about 10.Moreover, a probe can define any cross sectional shape, e.g., round,square, oblong, triangular, rectangular, etc.

As utilized herein, the term “ultrasound device” generally refers to adevice that includes an ultrasound transducer therein and that can beutilized in conjunction with a probe, but does not necessarily includethe probe itself. For instance, an ultrasound device can include a probeguide as an attachable or permanent component of the ultrasound device,and a probe can be utilized in conjunction with the ultrasound device toaccess a subdermal site by guiding the probe through the probe guide ofthe ultrasound device.

Detailed Description

According to one embodiment, disclosed herein are ultrasound devices andmethods for use in accurately forming a virtual image of a probe inconjunction with a sonogram during a medical procedure. Morespecifically, disclosed herein are ultrasound devices that can include adetector for detecting the location of a target associated with a probewhile the probe is hold or moved within a probe guide of the ultrasounddevice. A detector can be in communication with a processor that canutilize information received from the detector with regard to targetlocation and accurately identify the location of the probe tip basedupon the information. A processor can also be in communication with amonitor and can create an image of a virtual probe on the monitor, forinstance in conjunction with a sonogram. Beneficially, disclosedultrasound devices can accurately correlate the image of the virtualprobe tip with the location of the actual subdermal probe tip.

Utilizing an ultrasound device incorporating a probe guide, a probe canbe guided such that the probe tip approaches a subdermal site that canbe visualized on the scanned plane of a sonogram. For instance, theprobe tip can travel on a path that defines a known correlation withsound waves emitted by the ultrasound transducer, e.g., coincident inthe scanned plane, parallel to the scanned plane, or intersecting thescanned plane at a point. When utilizing the ultrasound device, the pathof the probe to the subdermal site can be known: the probe will advancetoward the subdermal site on a straight line and at a predeterminedangular relationship to the ultrasound housing base from the probe guideopening to the subdermal site that is imaged by the ultrasound. Thus,the path of the probe and the scanned plane of the sonogram image canboth be defined by the orientation of the ultrasound transducer and canbe coordinated on the subdermal site. In order to strike the site, theprobe tip can be guided along this known path the desired distance.Beneficially, an ultrasound device can be formed so as to beconveniently utilized by a single operator who can insert a probe usinga probe guidance system and also control the ultrasound transducer so asto see the sonogram and a virtual image of the probe overlaid on thesonogram in real time during the procedure.

An ultrasound device can incorporate a visualization system that can beused to create an image of a virtual probe that accurately correlateswith the actual probe as it is being guided to a subdermal site andwhile it is being held at the site. Through utilization of avisualization system, the path of a probe and hence the location of theprobe tip can be more clearly known in relation to subdermal site imagedby an ultrasound device.

In accord with the present disclosure, an ultrasound device can includea detector that can register the location of a target that is associatedwith the probe in the probe guide. This information can beelectronically communicated to a processor and processed with input data(e.g., the length of the probe, etc.) and displayed as a real time imageof a virtual probe in conjunction with a sonogram, i.e., the two images,the image developed from the data obtained by the detector, and thesonogram developed from the data obtained from the ultrasoundtransducer, can be displayed on the same monitor. Because the virtualprobe location is correlated with the actual probe location, thelocation of the probe tip in relation to the subdermal site and thestriking of the subdermal site by the probe tip can be seen in real timeby an operator watching the virtual probe on the monitor during theprocedure.

In general, any suitable detector can be utilized in disclosed devicesfor detecting the target that is associated with the probe. Forinstance, a detector can utilize infrared (IR), ultrasound, optical,laser, magnetic, or other detection mechanisms. In addition, thelocation of a detector is not critical to a device, save that it iscapable of detecting the target that is associated with the probe. Inaddition, the target can be any suitable item. It can be all or aportion of the probe itself, or can be directly or indirectly attachedto the probe.

FIG. 1A illustrates one embodiment of a magnetic based detection systemas may be utilized. As can be seen, an ultrasound device 200 can includea handle 102, a post 204, and a base 206. The base 206 can define aprobe guide 126 therethrough. An ultrasound transducer 110 thattransmits and receives ultrasonic waves can be located in base 106. Anultrasound device 200 can include a series of sensors 201 that form adetector along a length of post 204. Sensors can be sensitive to thepresence of a target 205 that can be attachable to a probe 254 which canbe, for example, a needle. In the magnetic based detection system,sensors 201 can be Hall effect sensors that are sensitive to a magneticfield and target 205 can include one or more magnets. One exemplaryembodiment of a magnetic based detection system as may be incorporatedin disclosed devices is describe in U.S. Pat. No. 6,690,159 to Burreson,et al., which is incorporated herein by reference.

The sensors 201 can be arranged in one or more rows extending lengthwisealong the post 204, which is the direction along which the probe willmove during insertion, herein defined as the X direction, as shown inFIG. 1A. As is known, the presence of a magnetic field can induce avoltage in a Hall effect sensor that is proportional to the size of themagnetic field. The voltage of each sensor 201 can be electronicallyscanned and processed to determine the location of the target 205relative to the sensing array (i.e., the detector). Processing caninclude grouping the sensors 201 and providing their outputs to a seriesof multiplexers which, in turn, are connected to a processor includingsoftware for analyzing the outputs and determining the location of thetarget 205 with regard to the entire sensor array. As the distance fromthe target 205 to the tip of the probe 254 is constant and known, theprocessor can likewise compute the location of the tip of probe 254.

The processing of the sensor outputs can include determining whichsensor 201 has the highest (or lowest, depending upon the magnetic fieldorientation) voltage output in a recognized grouping, corresponding tothe location of the magnetic target 205. In one embodiment, a processorcan analyze the output of the sensor having the highest voltage outputand a predetermined number of sensor(s) to each side. The analog outputsof the sensors can be converted to digital output according to knownmethodology that can then be evaluated to determine the target location.

Other methods can also be used to determine a set of sensors to evaluatefor position. One such method is correlation. In this method, a vectorof values corresponding to the desired signal can be mathematicallycorrelated against the vector signal set from scanned sensors 201. Apeak in the correlation signal can indicate the center of the desiredsensor set to evaluate.

Of course, the detection system need not utilize the peak signal andadjacent Hall sensors, but instead or in addition, sensors can evaluatethe zero crossing signal that can result from using combinations ofnorth and south magnets.

Referring again to FIG. 1A, the magnetic target 205 can be mounted atthe base of syringe 207 in conjunction with probe 254. The magnetictarget 205 can be mounted on a base plate of magnetically permeablematerial. By incorporating a base plate of magnetically permeablematerial beneath the magnetic target 205, the magnetic flux lines can beconcentrated in a direction away from the base plate. Except at veryclose range, the greatest magnetic flux density can be present at thecenter of the magnet and extend perpendicular thereto, e.g., parallel topost 204 in the X direction. In general, the flux density decreases as anear Gaussian distribution function as one proceeds away from the magnetcenter line in the plane of the magnet. The field decreases in a nearhyperbolic function as one proceeds away in a direction perpendicular tothe magnet face. More details concerning suitable magnet assemblies aredescribed in U.S. Pat. Nos. 5,285,154 and 5,351,004, both of which areincorporated herein by reference.

While the general construction shown in FIG. 1A can be used, it shouldnot be considered to be limiting. In this particular embodiment, thetarget incorporates a magnet, with a magnetic field having a fluxdensity which has a maximum at or adjacent to the center of the magnetand which decreases as a function of the distance moved away from themagnet. A single thin magnet can be used, or an array of magnets locatedside by side. The magnet or array of magnets then can be mounted inconjunction with a probe 254.

The magnetic material of target 205 can be any suitable material thathas a high enough energy to be detectable over the distance between thetarget 205 and the sensors 201. A non-limiting list of suitablematerials can include, without limitation, samarium cobalt, neodymium,or iron boron.

In one embodiment, a row of sensors 201, e.g., sensors of Hall effecttransducers, can be placed side by side in a single row in the Xdirection along the post 204, as illustrated in FIG. 1C. In onepreferred embodiment, the sensors 201 can be located close to eachother. However, the distance between adjacent sensors can be affected byconnection pins, casings, housings in which they are mounted, etc. Forexample, a small sensing component can be mounted in conjunction withpins or contacts that project from a housing for connection to a supplyvoltage, ground and output, respectively. Thus, even if housings areplaced end to end with their pins projecting in the same or alternatedirections, there will be a certain center to center distance betweenadjacent sensors. This distance can be reduced by providing an array ofsensors that are canted at an angle to the sensing or X direction, andare provided in two rows with the sensors staggered relative to eachother, as illustrated in FIG. 1B. This can decrease the center to centerdistance between adjacent sensing components for increased accuracy of adetector. Of course, other arrangements of the individual sensors 201forming an array along post 204 are likewise encompassed in the presentdisclosure.

The Hall effect sensors can operate at a typical supply voltage of about5 volts. The sensors can be designed to provide a known output voltage,e.g., about 2.5 volts, in the absence of a detectable magnetic field.The presence of a south pole magnetic field will increase the outputvoltage above the output voltage by an amount proportional to themagnetic field applied within a predetermined range of magnetic fieldstrength. Conversely, the application of a north pole magnetic fieldwill decrease the output voltage from its quiescent value proportionalto the magnetic field applied. Thus, for a given sensor, the outputvoltage can be directly correlated to the magnetic field strength.Moreover, as the magnetic field strength decreases with distance fromthe magnet, the output voltage of a sensor can be directly correlated tothe distance between the sensor and the magnet.

According to one embodiment, all of the sensors 201 can be mounted on asingle printed circuit board. The printed circuit board also can includemultiplexers for scanning of the outputs of the sensors. For example, inthe case of 64 sensors, eight eight-port multiplexers can be used andcoupled to a processor. A ninth multiplexer can be used to take theoutput of the eight multiplexers to one output for an analog-to-digitalconverter.

Each multiplexer can receive the outputs from eight of the Hall effectsensors and can provide a selected output on a line to a processor. Theprocessor can include an analog-to-digital converter that, incombination with the multiplexers, scans the outputs of the sensors andconverts the signals to digital form. The processing unit can also storean algorithm by which the Hall array outputs (i.e., the location of thetarget) can be processed to determine the location of the tip of theprobe relative to the sensor having the reading that locates thatparticular sensor closest to the center of the magnetic target 205, forexample, the sensor closest to the center of magnetic target can be thesensor obtaining the highest voltage output reading.

In one embodiment, processing of the outputs of the sensors 201 isaccomplished by scanning all sensor outputs and determining which ofthem has the highest value. For this purpose, highest means the maximumdifference from the quiescent value, i.e., the degree to which theoutput voltage has been shifted up or down from the quiescent voltageof, e.g., 2.5 volts. Highest value can also refer to the point in thearray where a predetermined signal vector produces the highestcorrelation against the scanned sensors. The outputs of a predeterminednumber of sensors at each side of the highest signal can also beconsidered, such as three sensors at each side or four sensors at eachside. The outputs of the remaining sensors can be ignored or can beincorporated, as desired. This predetermined number of outputs can thenbe used to calculate the location of the magnetic target 205 and alsothe tip of the probe 254 that is a known distance from the magnetictarget 205. The accuracy of the measurement in the X direction can bemaximized according any suitable methodology. For instance, thegeometric arrangement of the sensors can be optimized, as discussedabove, to limit the space between adjacent sensors, and the processoralgorithm or algorithms used to convert the input signals to distancemeasurement can be adjusted to reflect the highest voltage output fromany individual sensor depending upon its geometric location in the arrayand with respect to the magnetic target at its closest proximity.

Input information provided to a processing unit can include informationconcerning the position of each individual sensor. This can be by sensornumber, for example, “1,” “2,” . . . , “64” for a 64-sensor array, whichthen can be converted to a location value based on the position of thatsensor along the length of the post 204. One simple algorithm forcalculating the position of the probe tip from the selected outputs isrepresented as follows: The sensor having the highest output is labeled“S,” and the system is designed to consider the outputs of three sensorsat each side. Accordingly, such additional sensors can be labeled S−3,S−2, S−1, S+1, S+2 and S+3. The sensor number can be multiplied by itsrespective output, and the mean value determined for the selectedsensors. This value then can be converted to a distance or locationvalue for the tip of the probe, as the processing unit can include asinput data the distance from the target magnetic material 205 to theprobe tip. Similarly, if the conversion of sensor number to locationalready has been made, the location is weighted by the output of thecorresponding sensor, and the mean value determined and used as theindication of the location of the probe tip.

However, the above method assumes linear proportionality in variation ofmagnetic field strength away from the target in the sensing direction.In actuality, the variation is nonlinear, and more nearly a Gaussiandistribution. Consequently, a more accurate result can be obtained byfitting the selected data to a nonlinear function such as a Gaussiandistribution curve. In this computation, one of the parameters is themean of the Gaussian fit, which can correspond to the target location.Commercially available software can be used to calculate an appropriateGaussian distribution fit, such as TableCurve 2D, available from SPSSInc. Thus, the algorithm can include the step of calculating theGaussian distribution fit and determining the mean.

Other parameters of a Gaussian distribution that can be taken intoaccount can include the spread of the Gaussian signal and the amplitude.Spread calculations can be used for error correction or fault detection.If a given sensor or sensors influence the fit of a distribution curvebeyond reasonable parameters, that sensor or sensors can be assumed tobe providing erroneous data and be ignored.

Approximate Gaussian distributions can be calculated with as few asthree sensors, i.e., a maximum strength sensor and one at each side.Using greater numbers of sensors to perform the calculation can increaseaccuracy, and can also allow more flexibility in ignoring sensors whosevalues vary unreasonably from other sensors in the calculation set, forerror correction and fault detection purposes.

Signals from the sensors 201 can create a data stream which can be sentto a processor. A processing unit can be internal or external to anultrasound device 200. For example, data from sensors can be sent to astandard lap top or desk top computer processor or part of aself-contained ultrasound device as is known in the art. A processor canbe loaded with suitable recognition and analysis software and canreceive and analyze the stream of data from sensors.

The analysis of data carried out by the processor and associateddetermination of probe tip location and formation of the virtual probeimage can be improved by taking into account variations from an idealsystem. For instance, each ultrasound device can vary somewhat fromideal in placement and output of individual sensors used in a sensorarray. This potential effect can be mitigated through determination of avoltage offset value for each sensor, and the inclusion of that value inthe processor programming, such that the data obtained from each sensoris processed in conjunction with the voltage offset value for thatsensor.

For instance, each sensor can be scanned in the absence of a magneticfield, and the amount of voltage offset, if any, can be determined foreach sensor. This voltage offset value can take into account both anyinnate variation in output of the sensor as well as any variation due toslight mislocation of a sensor when being placed on an ultrasound deviceduring manufacturing. The calculation of the position of the magnetictarget along the sensor array can include the adjustment of a sensoroutput by its offset amount.

Other variations in individual ultrasound devices due to manufacturingcan be accounted for as well through determination of offset values thatcan be programmed into the processor. For instance, and with referenceto FIG. 1A, the distance from the surface 108 to the probe guide exit atthe top of base 206 and the location of the sensor array with referenceto the probe guide can vary slightly from one ultrasound device toanother. This can be accounted for by including a value in the processorprogramming that represents this variation. S_(offs) is utilized in thepresent disclosure to represent this variation. It includes two parts:one part is defined by the geometry of the ultrasound device and is thedistance from the skin contacting surface of the device 108 at the exitof probe guide 126 to the beginning of the sensor array 103 (i.e., thefarthest point of the sensor array from the base). The other componentis dependant upon the manufacturing precision: how accurate the sensorarray was placed on the ultrasound device in relation to the surface ofthe ultrasound transducer. This component is variable and will bedifferent for every manufactured probe, but this difference is verysmall. This value can be obtained by a calibration process and can beprovided to the processor programming algorithm.

An ultrasound device can also be programmed to include more than oneS_(offs) value, depending upon the application. For instance, and asdescribed further below, an ultrasound device can be utilized with asterilizable shield, so as to be used in a sterile procedure. In thisembodiment, a device 200 can be enclosed within a shield, which canalter the value of S_(offs). Such variations can be easily accountedfor, however, for instance, by providing a switch on the ultrasounddevice, which can provide the input value for S_(offs) to the processor,e.g., when the switch is set for a sterile application, the value forS_(offs) takes into account the use of a shield about the ultrasounddevice 200.

In addition to standard methods for improving accuracy of a system, asdescribed above, a system can correct for shifts in the locationdetermination that can be brought about due to the flexibility of aprobe. By way of example, FIG. 2 illustrates the flexing of a probe 254that could occur during use if, for instance, a user inadvertentlypushes the syringe 207 away from post 204 during a procedure. As can beseen, this can cause the portion of the probe 254 above the probe guideto bend. As the probe is flexible, the probe will straighten within theprobe guide and proceed to the subdermal site along the path defined bythe probe guide. This flexibility of the probe during delivery can leadto sensor information provided to the processor that differs from whenthe probe is aligned with the probe guide, which in turn can cause theprocessor to present a false location of exactly where the tip of theprobe is on a sonogram.

To better illustrate this condition, FIG. 3A overlays a probe 207 a thatis aligned with the probe guide 126 in the X direction and a probe 207 bthat has been pushed a distance out of alignment and is flexed away frompost 204 above the probe guide 126. When the probe is in the position of207 a, the magnetic target 205 will be determined by the array ofsensors 201 to be at the marked location A. However, when the probe isin the position of 207 b, the array of sensors 201 will obtain adifferent view of the magnetic field, which can lead to thedetermination of the virtual probe tip at a point that differs from thelocation of the actual probe tip at the subdermal site. For instance,the highest magnetic field strength can be determined by the sensorarray to be at B, rather than at A, when the probe is flexed. This canlead to an error in the correlation of the virtual probe image with theactual probe.

The probe tip location of the virtual image is determined by theprocessor based upon the combination of the location of the magnetictarget as determined by the sensor array and the known distance betweenthe magnetic target and the probe tip. Any flexing of the probe 254 doesnot effect the location of the actual subdermal probe tip, it merelytilts the magnet away from the post 204.

FIG. 3B illustrates in greater detail how the flexing of the probe canlead a system to locate a virtual probe tip at a location that variesfrom the location of the actual probe tip. This variation is affected bytwo distinct aspects. First, the magnetic field determination by thesensor array will locate that magnet at point B rather than at point A,as discussed. This will have the effect of placing the virtual probe tipabove the actual probe tip (too shallow). In addition, the bending ofthe needle will alter the geometry of the system, i.e., the length L_(B)is longer than the length of the chord 239 of the bent probe. Thestraight projection of the bent probe segment back to the sensor arraywill locate the magnet at point C, as shown in FIG. 3B, rather than atpoint A (where the magnet is located when the probe is not bent). Thiswill have the effect of placing the virtual probe tip beneath the actualprobe tip (too deep). Disclosed systems can take both of these affectsin to account to accurately correlate a virtual image of a probe withthe actual subdermal location of the probe.

The alteration in sensor reading that will occur when a probe is flexedout of alignment can be accounted for by the inclusion of a set ofcorrelation factors into the processor algorithm. A set of correlationfactors determined for a single ultrasound device can generally beapplicable to all similar ultrasound devices (i.e., devices of a similarsize and shape, a similar sensor array and location, etc.). Thus, a setof correlation factors need not be determined for every individualdevice (though this is certainly an optional embodiment). Rather, a setof correlation factors can be determined for a single type of device,and those correlation factors can then be incorporated in the processoralgorithm for all ultrasound devices of a similar type.

To describe the determination of the correlation factors, certainterminology is utilized herein including:

-   -   L_(B)—Length of the bent portion of the probe (e.g., a needle).    -   S₀—The location of the magnetic target as would be determined by        the sensor array were the probe to be properly aligned with the        probe guide along the X axis.    -   S_(H)—The location of the magnetic target as determined by the        sensor array when the probe is flexed out of this alignment.    -   L_(C)—The length of the probe guide as measured from the base        surface of the probe guide 108 to the top exit from the probe        guide (where the probe begins to be bent out of alignment).    -   S_(offs)—The calibrated distance from the skin contacting        surface of an ultrasound device to the distal end of the sensor        array.    -   H—A level index that represents the number of defined steps (or        levels) out of alignment the probe is flexed. The level index H        can be in any direction from the detector, i.e., in the Y axis,        the Z axis or some combination thereof.

An equation to describe the correlation of a flexed probe has beendetermined to be:S ₀ =S _(H)+(a*H+c)L _(B) +b*H+d

where S₀, S_(H), H, and L_(B) are as described above and a, b, c, and dare a set of correlation factors determined experimentally for each typeof ultrasound device, an example of which is explained in further detailbelow.

This general equation has been determined experimentally by a best fitprocess, as described below. Beneficially, this equation can hold forany ultrasound device in which a probe that is ideally aligned with aprobe guide and an ultrasound transducer as described herein can be bentout of alignment such that a portion of the probe is bent away from thedetector. To accurately portray the location of the virtual probe tip ona formed image so that it is aligned with the actual subdermal locationof the probe tip, this equation can be utilized by the processorsoftware to correlate the measured value of S_(H) with an aligned valueS₀.

The number of correlation factors encompassed in the equation andprogrammed into the processor can vary, as desired, with the utilizationof more correlation factors providing a higher correlation between thevirtual image and the actual location of a subdermal probe. Forinstance, in one embodiment, fewer correlation factors can be utilized,and the processor instructions can include solving the equationS ₀ =S _(H) +a*H*L _(B) +b*H.which incorporates only the a and b correlation factors. Similarly, thecorrelation equation can utilize only the a or the a, b, and ccorrelation factors in an equation. Moreover, additional factors can beincorporated in an equation, as would be known to one of skill in theart, with a improved alignment possible between the virtual probe tipand the actual probe tip when utilizing more correlation factors in theequation.

The values for S_(H) and H can be obtained from the sensor during use.Specifically, S_(H) is the value obtained by the sensor for the magnetictarget location, and H can be obtained by the variation in the measuredparameter (e.g., voltage) from the expected value when the probe is notbent. For instance, when the probe is not bent, and H=0, the voltagevalue obtained by the sensor at the magnetic target location will matchthe expected value. When the probe is flexed out of alignment, however,the highest voltage level obtained by the sensor can be less thanexpected. It is a simple matter to equate this drop in voltage with alevel index value H, which can then be utilized in the correlationdetermination.

The value of L_(B) is not directly obtainable by the sensor readings, asare S_(H) and H. However, the length L_(B) can be written in terms thatare obtainable by the sensor reading. SpecificallyL _(B)=(S _(offs) −S _(H))−L _(C)

By substituting this equation into the equation for determining S₀, avalue for S₀ can be obtained in terms of parameters that are eitherpredetermined for each ultrasound device (e.g., L_(C), S_(offs)) ordeterminable from the sensor reading (S_(H), H).

Specific values for the correlation factors a, b, c, d, can beexperimentally determined, as described in the examples section below.For example, the correlation factors can be:

a—between about −0.045 and about −0.055, for instance about −0.050;

b—0 or between about 4 and about 5, for instance about 4.30;

c—0 or between about 0.02 and about 0.03, for instance about 0.028;

d—0 or between about −0.5 and about −0.06, for instance about −0.053.

The correlation equation can be included in the instruction provided tothe processor in the form of software, and the location of a virtualprobe tip imaged in conjunction with a sonogram can be correlated withthe location of an actual subdermal probe tip.

Upon determination of a value for H from the readings obtained by thesensor, the distance the target magnet has traveled away from alignmentcan be determined. In one embodiment, a device can include a warningsignal to alert a user should the magnet be moved beyond a predeterminedlevel. For instance, should a probe be flexed such that the level indexH becomes greater than, e.g., 5 or 6, an alarm can be triggered by theprocessor, so as to alert a user that the probe has been moved out ofthe desired position. An alarm can be visual, auditory, tactile, or anycombination thereof. For instance, a signal light can be turned onshould the level index determined at the processor exceed apredetermined value.

According to another embodiment, correlation of the virtual probelocation as determined by the motion detector with the actual probelocation can be determined through examination of the individual sensoroutputs. As previously discussed, in one embodiment, a plurality ofsensors are examined for determination of the location of the magnetictarget. Specifically, a number of sensors both above and below a centralsignal (i.e., that signal location corresponding to the magnet locus)can also be considered, such as three sensors at each side or foursensors at each side. With reference to FIG. 1A, when a probe is alignedwith the probe guide opening along the X-axis and generally parallel tothe array of sensors 201 in post 204, the variation of magnetic fieldstrength in the sensors above and below the target will be known, and inone embodiment, can be generally equivalent to each other (see, e.g.,FIG. 4A, which illustrates one embodiment of the magnetic field strengthalong the X-axis, with the magnet at point A). For instance, themagnetic field strength can decrease according to a Gaussiandistribution in both directions from the highest signal at the centersensor to the individual sensors that are farther away from the highestsignal strength. Even if the decrease above and below the highest signalstrength is not equivalent, the ideal decrease in both directions can beknown. Upon flexing of a probe away from the desired alignment, themagnetic field strength variation will be altered from the idealdistribution as the magnet and the magnetic field become tipped ascompared to the sensors, as shown in FIG. 4B. Thus, this distributioncurve and the variation from ideal of the magnetic field distributioncurve can be utilized in another embodiment to determine the amount offlex from the aligned position of a probe.

While the above description is specific for magnetic sensors located onthe post of a device, it should be understood that the presentdisclosure is not limited to this specific sensor type. Any other typeof sensor can be utilized in disclosed ultrasound devices. For instance,FIG. 5A illustrates sensors 301 located on the base 306 of ultrasounddevice 300. Sensors 301 can be on the surface of base 306 or within thebase 306, depending upon the sensor type, the materials of the base 306and so forth. Sensors 301 are directed toward a target 305 associatedwith probe 354. Sensors 301 can utilize any suitable format, e.g.,optics, sonics, proximity sensors, magnetics, etc., and determine thedistance from the sensors 301 to the target 305. Input data to aprocessor can include the distance from the target 305 to the tip ofprobe 354 so as to accurately portray the location of the actual probein forming a virtual probe image.

When the probe 354 is aligned with the probe guide opening 339 andcentered above the probe guide opening, as illustrated in FIG. 5A, thetwo sensors 301 will obtain equivalent distances. FIG. 5B illustrates atop view of the device including two sensors illustrated in FIG. 5A. Ascan be seen, ultrasound device 300 includes two sensors 301 radiallyopposite one another across the probe guide opening 326. Upon flexing ofthe upper portion of a probe 354, as shown in FIG. 6, the distancemeasured from one sensor will differ from that of its counterpart thatis opposite across the probe guide opening, as shown. Thus, theprocessor can obtain data and determine that the distance from eachsensor to the target is no longer equivalent, as it should be.

According to this embodiment, the processor can include a correlationalgorithm, similar to that described above for a sensor array located ona post parallel to the aligned direction of probe travel, so as toaccurately locate the tip of the virtual probe image. For instance, anS_(offs), as described above can be obtained for each device, based uponthe variations in manufacturing between devices, and the measured sensorarray result for the location of the target, S_(H), can be corrected toprovide S₀, i.e., what that result would be if the probe 354 were notflexed out of the aligned position. A series of correlation factorsexperimentally determined for an ultrasound device can be programmedinto the processor for application to all devices of that same type. Inother words, the correlation factors obtained can be a permanent part ofthe processor, and each processor need not be specifically reprogrammedfor every device.

An ultrasound device can include a plurality of sensors at the base. Forinstance, FIG. 5C illustrates a top view of an embodiment in which anultrasound device includes multiple sensors 301 surrounding a probeguide opening 329. When a probe is aligned with the probe guide openingin the X direction, all of the sensors will have an essentiallyidentical reading as to distance from the sensor to the target. If thetarget is pushed in any direction and thus out of alignment, the sensorswill register the target at a variety of different distances, alertingthe processor to the misalignment. The correction algorithm can besimilar to that described above for a two-sensor system, but canincorporate additional parameters for the other sensors.

A processing unit can also include standard imaging software as isgenerally known in the art to receive data from an ultrasound transducerthat is a part of the ultrasound device in addition to software that canprocess readings from a detector with regard to misalignment of a probein the device, as described, and form a virtual image on a monitor thataccurately portrays the location of the actual probe being insertedsubdermally. Input data for the processor, such as the length of theprobe, offset values, correlation factors, and so forth, can be enteredinto the processor by the user at the time of use or can bepreprogrammed into the system as default data, depending upon the natureof the data, as discussed. Through analysis of the data stream receivedfrom both the detector and the ultrasound transducer, a processor cancalculate the position of the probe tip relative to the ultrasoundtransducer, relative to a sensor, relative to the skin contactingsurface of the device, or relative to any other convenient referencepoint. A processor can communicate this position information digitallyto a monitor and the information can be displayed on the monitor such asin a numerical format or as a real time image of a virtual probe.Moreover, this data can be illustrated in conjunction with, e.g.,overlaid on, the sonogram that displays an image of the subdermal site,such as a blood vessel.

In such a manner, disclosed ultrasound devices can be utilized toactually show the approach of a probe toward a subdermal site on amonitor throughout the entire procedure. In addition, disclosed devicescan be utilized to ensure the probe tip remains at the subdermal siteduring subsequent procedures. For example, as long as the detector isinteracting with the target the virtual image of the probe can remain onthe monitor. Thus, any motion of the probe tip in relation to the thesubdermal site can be noted by an observer, even following the clampingof the probe within the probe guide.

Any type of ultrasound transducer as is generally known in the art canbe incorporated in ultrasound devices as disclosed herein. By way ofexample, a piezoelectric transducer formed of one or more piezoelectriccrystalline materials arranged in a two or three-dimensional array canbe utilized. Such materials generally include ferroelectric piezoceramiccrystalline materials such as lead zirconate titanate (PZT). In oneembodiment, the elements that form the array can be individual electrodeor electrode segments mounted on a single piezoelectric substrate, suchas those described in U.S. Pat. No. 5,291,090 to Dias, which isincorporated herein by reference thereto.

In general, an ultrasound transducer can be formed of multiple elements.However, single crystal ultrasound transducers are also encompassed bythe present disclosure. The use of a multiple element ultrasoundtransducer can be advantageous in certain embodiments, as the individualelements that make up the transducer array can be controlled so as tolimit or prevent any break or edge effects in a sonogram. For instance,the firing sequence of individual crystals can be manipulated throughvarious control systems and prevent any possible ‘blind spots’ in asonogram as well as to clarify the edges of individual biologicalstructures in the sonogram. Such control systems are generally known inthe art and thus will not be described in detail.

Referring again to FIG. 1A, the scanned plane (i.e., the plane of thesonogram) can be the geometric central plane of the beam transmittedfrom the ultrasound transducer 110. In one preferred embodiment, thepath of a probe that is guided through probe guide opening 126 can bewithin the scanned plane. This is not a requirement of the presentdisclosure, however. For instance, the path of a probe passing throughprobe guide opening 126 can be at an angle to the scanned plane suchthat it intersects the scanned plane at a point. By way of example, theline defined by the path of a probe passing through the probe guideopening 126 can be at an angle of ±1° to the scanned plane in oneembodiment, at an angle of ±0.6 degrees in another embodiment, or at alesser or greater angle in another embodiment. For instance, a linedefined by the path of a probe passing through the probe guide openingcan be at an angle of ±10, °±20°, ±45°, or even greater, in otherembodiments.

An ultrasound device as encompassed herein can have any convenientgeometry. For instance, and with reference to FIG. 1, handle 102 can beset at an angle to post 204 so as to be comfortably held in the handwhile the device is being utilized. For instance, in the illustratedembodiment, handle 102 is about 90° to post 204, though this angle canbe varied as desired. Moreover, in another embodiment described furtherherein, an ultrasound device need not include an extending handleportion at all.

The base 206 of an ultrasound device can also have any convenientgeometry. For instance, the skin contacting surfaces 108 can be angled,as illustrated, or can be planar from edge to edge. When present, theangle of a skin contacting surface 108 can vary from 0° to about 30°, orfrom about 10° to about 20° in another embodiment. In yet anotherembodiment, a skin contact surface can define an angle opposite to thatillustrated in FIG. 1, i.e., the skin contacting surface 108 can beconvex. A skin contacting surface can also include curvature, e.g., candefine an arcuate profile along the length or width of the surface. Thefootprint shape of the skin contacting surface 108 may be rectangular,round, oblong, triangular, etc. With regard to size, the skin contactingsurface 108 can be, e.g., between about 0.5 inches and about 6 inches onits greatest length. In one embodiment, the skin contacting surface 108can be about 0.5 inches on its greatest width and can promote stabilityof the device during use. In other embodiments, it can be larger,however, such as about 1 inch on its greatest width, about 2 inches onits greatest width, or even larger.

The shape of all or a portion of an ultrasound device may beparticularly designed to fit specific locations of the anatomy. Forexample, a device may be shaped to be utilized specifically forinfraclavicular approach to the subclavian vein, approach to theinternal jugular vein, specific biopsy procedures including, withoutlimitation, breast biopsy, thyroid nodule biopsy, prostate biopsy, lymphnode biopsy, and so forth, or some other specific use. Variations inshape for any particular application can include, for example, aspecific geometry for the footprint of a base, alteration in the size ofpost and/or handle, as well as variation in angles at which variouselements of a device meet each other.

An ultrasound device can be utilized in conjunction with a sterilizableshield, for instance in those embodiments in which a probe is intendedfor use in a sterile field. A sterilizable shield can be formed ofsterilizable materials as are generally known in the art. In oneembodiment, a sterilizable shield can be formed of single-use materialssuch as polymeric materials, and the entire shield can be properlydisposed of following a single use. In another embodiment, asterilizable shield can be utilized multiple times, in which case it canbe formed of a material that can be properly sterilized between uses. Asterilizable shield can be formed of a moldable thermoplastic orthermoset polymeric material including, without limitation, polyester,polyvinyl chloride, polycarbonate, and so forth.

FIG. 7 illustrates one example of a sterilizable shield 130 as may beutilized to encase an ultrasound device. Sterilizable shield 130 caninclude a lower section 132, details of which are shown in FIG. 8, andan upper section 134, details of which are shown in FIG. 9.

With reference to FIG. 8, shield section 132 can include a base 136formed of an ultrasonic transmissive material. Base 136 can be of anysuitable size and shape, but formed such that an ultrasound transducerhousing base may be seated firmly in shield base 136. Generally, a smallamount of an ultrasonic gel can be placed between the bottom surface ofthe transducer housing base and shield base 136 during seating toprevent any air between the two and promote transmission of ultrasonicwaves.

Arising out of shield base 136 is guide post 138. Guide post 138 definesat least a portion of a probe guide 139 therethrough. Probe guide 139extends uninterrupted completely through both guide post 138 and shieldbase 136. Guide post 138 can include tabs as shown, or other formationssuch as hooks, insets, or the like that can be utilized to properlyassemble shield base 136 about an ultrasound transducer housing. In oneembodiment, guide post 138 may include a removable cap (not shown) forprotection of the interior sterile surface of probe guide 139 duringassembly of shield 130 with an ultrasound transducer housing. As shownin FIG. 9, section 134 defines the terminal portion 151 of probe guide139. Terminal portion 151 is sized so as to snugly reside over the topof guide post 138 of section 132 and form uninterrupted probe guide 139extending from the top surface of portion 160 of section 134 to thebottom surface of base 136 of section 132.

As can be seen, shield section 132 can also include tabs 140, 142, 144,etc. that can be utilized in properly seating an ultrasound housingwithin shield section 132 as well as aligning shield section 132 withshield section 134 when assembling the complete shield 130 about anultrasound transducer housing.

Tabs 140 on shield section 132 can match corresponding notches 141 onshield section 134 shown in FIG. 9. Together tabs 140 and notch 141 forma fastener that can secure shield section 132 and shield section 134 toone another. During assembly, tabs 140 can snap into notch 141 tosecurely fasten the two sections together and prevent separation of thesections 132, 134 during use. Of course, a shield can include additionalfasteners at other locations between the two sections, or can include asingle fastener at an alternative location, as would be known to one ofskill in the art.

In order to disassemble shield 130, tabs 140 can be simply pinchedtogether and slid out of notch 141. In another embodiment, a single-usefastening mechanism can be employed to secure sections of a sterilizableshield to one another. According to this embodiment, in order todisassemble a shield following use, the tabs of the fastener can bepermanently disabled upon disassembly of the shield. For instance, tabs140 and/or notch 141 can be permanently broken away from the shield by apulling or twisting motion, allowing the shield sections to come apartand also ensuring that the shield, which is no longer sterile, cannot beutilized again. Any method that can ensure that a fastener can only beutilized a single time may alternatively be utilized.

To assemble the illustrated sterilizable ultrasound device, anultrasound device 200 defining probe guide opening 126 shown in FIG. 1Acan be seated in section 132 of sterilizable shield 130 such that guidepost 138 extends through transducer housing probe guide opening 126. Asprobe guide opening 126 of ultrasound device 200 is slid over guide post138, tabs on guide post 138 can slide or snap into recesses of probeguide opening 126 (not shown), helping to properly seat ultrasounddevice 200 in section 132. After ultrasound device 200 is seated insection 132, section 134 can be aligned with section 132 and fastenedinto place to cover the top of ultrasound device 200. If a protectivecap covers the end of guide post 138, it can be removed during assemblyand maintain the sterility of the interior of the probe guide 139throughout the assembly process. Tabs 140 can snap or slide intorecesses notch 141 to fasten and secure section 132 and 134 together.

Following the above described assembly process, probe guide 139 canextend continuously from the top of portion 160 of shield portion 134through the shield base 136. Moreover, and of great benefit to thedevice, probe guide 139 can be sterile and within the probe guideopening 126 of ultrasound device 200.

Though illustrated as being formed of two separable sections, asterilizable shield can be hinged or can include additional sections, asdesired. For instance, a sterilizable shield can be formed of two,three, or more separable sections that can be assembled to enclose allor a part of an ultrasound housing and form a sterile barrier betweenthe enclosed housing and an exterior field. In another embodiment, asterilizable shield can be of a unitary construction. For instance, asterilizable shield can be of a pliant material that can enclose all ora portion of an ultrasound housing and form a sterile barrier betweenthe enclosed housing and an exterior field.

Referring to FIG. 7, the assembled sterilizable shield 130 can alsoinclude a clamp 156. During use, clamp 156 can firmly hold a probe 154in the probe guide and prevent motion of the probe 154 during aprocedure such as a catheter insertion, a biopsy procedure, fluidaspiration, or the like. Motion of the subdermal probe tip followinginsertion can be much less likely when the probe 154 is securely clampedto the probe guide of the sterilizable shield 130 and the ultrasounddevice is in turn held and stabilized by an operator as compared todevices in which a probe is simply held free-hand by an operator.

As can be seen in FIG. 7, a probe 154 can extend through a probe guide(not shown) of sterilizable shield 130. Clamp 156 sits atop the base 161of sterilizable shield 130 such that probe 154 passes through clampaperture 158 as shown. Co-owned patent application Ser. No. 12/576,498to Ridley, et al., which is incorporated by reference, describes oneclamp as may be incorporated with an ultrasound device. Any otherclamping action can alternatively be utilized. For instance, a clamp cantighten about a probe by a rotational motion of a clamping surface abouta clamp, as is illustrated in U.S. Pat. No. 7,244,234 to Ridley, et al.,which is incorporated herein by reference. Any relative motion between aclamp and a probe that can serve to firmly hold a probe in place througha friction hold, through physical interaction of probe/clamp segments,or through any combination thereof is encompassed in the presentdisclosure.

FIG. 10 illustrates another embodiment of an ultrasound device 800 thatis encompassed by the present disclosure. According to this embodiment,ultrasound device 800 can include a handle 802, a post 804, and a base806. Ultrasound device 800 also defines a lower surface 810, as shown.In this particular embodiment, however, the ultrasound transducerhousing does not include a probe guide opening. Instead, ultrasounddevice 800 is removably attachable to a second portion that defines theprobe guide opening. For instance, ultrasound device 800 can be utilizedin conjunction with a sterilizable shield that defines a probe guide.Moreover, the sterilizable shield can be formed of a single or multipleremovably attachable pieces.

FIG. 11 illustrates a sterilizable shield 930 that can be used inconjunction with an ultrasound device 800 illustrated in FIG. 10.Sterilizable shield 930 includes section 932 and section 961, whichdefines a probe guide for passage of probe 954 therethrough.Additionally, section 932 can be separable into two or more section.Section 961 can also include clamp 956 defining aperture 958 andformations 962, 963. Clamp 956 can rotate about pivot 964 for clampingprobe 954 in the probe guide. During use, section 961 can be attached tosection 932, for instance by use of aligned tabs and notches, and soforth, so as to attach the probe guide portion to the sterilizableshield.

Of course, any other arrangement of the individual portions of anultrasound device are encompassed within the present disclosure. Forinstance, in one embodiment, a section of an ultrasound device that doesnot define a probe guide opening, as illustrated in FIG. 10, can beremovably attached to a section that defines the probe guide opening andincludes the clamp, without enclosing the entire device in asterilizable shield. In another embodiment, a sterilizable shieldportion can cover only the skin contacting surface of an ultrasounddevice. For instance, a shield portion can snap onto the base of anultrasound device.

Another embodiment of an ultrasound device is illustrated in FIG. 12. Ascan be seen, ultrasound device 1000 does not include a handle portion.Such a device can be comfortably held by the rounded back portion 1002,with the skin contacting surface 1110 held against a subject. Ultrasounddevice 1000 can include some form of attachment, e.g., tabs, slots,hooks, etc, to attach a probe guide portion 1061 comprising clamp 1056to device 1000. When attached, the probe guide of portion 1061 can bealigned with an ultrasound transducer located in the base of ultrasounddevice 1000.

Presently disclosed ultrasound devices and methods may be utilized inmany different medical procedures. Exemplary applications for thedevices can include, without limitation

-   -   Central Venous Catheterization    -   Cardiac Catheterization (Central Arterial Access)    -   Dialysis Catheter Placement    -   Breast Biopsies    -   Paracentesis    -   Pericardiocentesis    -   Thoracentesis    -   Arthrocentesis    -   Lumbar Puncture    -   Epidural Catheter Placement    -   Peripherally Inserted Central Catheter (PICC) line placement    -   Thyroid Nodule Biopsies    -   Cholecystic Drain Placement    -   Amniocentesis    -   Regional Anesthesia—Nerve Block

Some of these exemplary procedures have employed the use of ultrasounddevices in the past, and all of these procedures, as well as others notspecifically listed, could utilize disclosed ultrasound devices toimprove procedural safety as well as patient safety and comfort, inaddition to provide more economical use of ultrasound devices.

The present disclosure may be better understood with reference to theExamples, provided below.

EXAMPLE 1

An ultrasound device as illustrated in FIG. 13 was utilized. The needleprobe 254 was flexed away from the post 204 of the device, as shown. Asensor array 103 of Hall effect sensors was located within the post 204.The sensors used were ratiometric linear Hall effect sensors availablefrom Allegro MicroSystems, Inc., model no. A1321. FIG. 13 also providesa top view 270 of the post 204, showing the curvature of the post toaccommodate the target magnet 205. The needle 254 was flexed byincreasing levels away from the post 204. Sensor array readings, S_(H),which can be converted to a location parameter by simple geometricconversion based upon the ultrasound device, are provided in the Table1, below. Data in each row were obtained with the same fixed position ofthe needle.

TABLE 1 Level H 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Meter 702.5 699696 692 689 readings 611 608 605 602 599 596 594 S_(H) 520 517 514 511509 507 506 504 502 500 499 497 496 460 458 455 453 451 449 447 446 444443 442 441 440 439 437 401 399 397 394 393 391 389 386 384 383 381 380378 377 376 375 374

As shown, flexing the needle (the more the needle is bent the higher islevel number H) reduces the sensor readings S_(H).

Best fit of the data, with precision better than 0.3 mm for levels from0 to 10, and better than 0.6 mm for levels 11-16) provided the followingequation:S ₀ =S _(H)+(a*H+c)*L _(B) +b*H+d

where

-   -   a=−0.051;    -   b=4.31;    -   c=0.0276;    -   d=−0.534.

EXAMPLE 2

FIG. 14 illustrates a geometric model utilized to describe the tilt of atarget magnet with the flexing of an attached probe from alignment witha probe guide. An assumption was made that the needle was bent with aconstant radius of R. (In this example, the value for the level index,H, has been converted to the distance from the sensor array to themagnet.) The following equations can be written:L _(B) =R*αh=2R*sin²(α/2)h+R _(M) =H+R _(M)*cos(α)

-   -   R_(M) is the magnet radius (11 mm in this example).    -   Thus,        H=[L _(B)*sin²(α/2)]/α−R _(M)*cos(α)

This equation was solved digitally, and the results for the values of α(in radians) are shown in Table 2, below.

TABLE 2 L_(B) = L_(B) = H (mm) L_(B) = 68 mm L_(B) = 58 mm L_(B) = 48 mm38 mm 28 mm 0 0 0 0 0 0 3.5 3.34 3.9 4.68 5.84 7.76 5.5 6.6 7.7 9.2211.44 14.92 7.5 9.84 11.44 13.64 16.78 21.64 9.5 13.04 15.14 17.96 21.9628 11.5 16.2 18.76 22.2 27.02 13.5 19.34 22.34 26.38

The results of Examples 1 and 2 were combined to provide a graph (FIG.15) illustrating the experimentally obtained values for the shift in thesensor reading due to the flexing of the needle (S₀−S_(H)) depend uponthe angle of the flex, α. As can be seen with reference to FIG. 15, thesensor reading shift can not be explained only by the tilt of themagnet, this shift also depends upon the distance between the magnet andthe sensors. Disclosed methods provide a route for accounting for thisshift during the formation of a virtual image and correlating theposition of a virtual image of a probe created on a monitor with theactual location of a subdermal probe.

EXAMPLE 3

A second set of data for S_(H), the output of the Hall effect sensorarray, were obtained utilizing a system similar to that described abovein Example 1. Raw data is provided below in Table 3. Best fit of thedata provided values of the correlation factors a=−0.051 and b=4.26.Thus, the correlation equations are as follows (the values for S_(offs)and S_(H) are in units of 0.1 mm, hence the conversion factor in theequation):L _(B)=(S _(offs) −S _(H))/10−L _(C),S ₀ =S _(H)+(4.26−0.051*L _(B))*H,

TABLE 3 L_(B) = L_(B) = H (mm) L_(B) = 68 mm L_(B) = 58 mm L_(B) = 48 mm38 mm 28 mm 0 203 306 404 501 597.5 3.5 199 296 397 493 588 5.5 196293.5 384 486 581 7.5 194 289.5 380 474 565 9.5 192 285.5 376 470 55811.5 189 281.5 373 464 13.5 184 276.5 371

Utilizing these correlation factors in the processing software, a testwas run. A needle of length 88.9 mm (3.5 inches) was used. A value ofS_(offs) was determined to be 685. A value of L_(C) was determined to be20.9 mm.

A device as illustrated in FIG. 13 including a detector was used. Thedetector provided the following readings:

S_(H)=400

H=5

-   -   From equation 1:        L _(B)=(685−400)/10+21.0=49.5 (mm)    -   From equation 2:        S ₀ −S _(H)=(4.26−0.051*49.5)*5=8.7

Through use of the correlation factors, the actual needle was determinedto protrude from the ultrasound device by a value ofdL _(B)=(S ₀ −S _(H))/10=0.87 mmmore than is determined by the meter with no correlation of the readingS_(H). This determination was confirmed by actual measurement of theprotrusion. Accordingly, when forming a virtual image of the needle onan ultrasound image, the location of the virtual needle tip can beaccurately located with use of the correlation factors in the processingcomponent of the system.

EXAMPLE 4

The system and correlation factors of Example 3 were utilized.Parameters measured by the detector included:

-   -   S_(H)=550    -   H=3

From equation 1:L _(B)=(685−550)/10+21.0=34.5 (mm)

From equation 2:S ₀ −S _(H)=(4.26−0.051*34.5)*3=7.5anddL _(B)=(S ₀ −S _(H))/10=0.75 mm

This determined value was confirmed through actual measurement of thedistance from the detector target to the tip of the needle.

It will be appreciated that the foregoing examples, given for purposesof illustration, are not to be construed as limiting the scope of thisinvention. Although only a few exemplary embodiments of this inventionhave been described in detail above, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention which isdefined in the following claims and all equivalents thereto. Further, itis recognized that many embodiments may be conceived that do not achieveall of the advantages of some embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

What is claimed is:
 1. A method for guiding a probe tip to a subdermalsite comprising: guiding a flexible probe through a probe guide of anultrasound device, the probe guide defining a probe path for the probeto follow to reach the subdermal site, the probe terminating in theprobe tip, the probe guide including a first end and a second end, thefirst end being closer to a skin contacting surface of the ultrasounddevice than the second end, the ultrasound device comprising anultrasound transducer in communication with a processor, the ultrasounddevice further comprising a detector for determining the location of atarget that is associated with the probe and is at a distance from theprobe tip, the detector being in communication with the processor, theprobe path including a predetermined alignment between the target andthe detector as the probe is guided through the probe guide; flexing aportion of the probe out of the predetermined alignment as the probe isguided through the probe guide, the flexed portion of the probe beingexternal to the probe guide and not subdermal; configuring the processorto determine the location of a virtual probe tip from the location ofthe target as determined by the detector and communicated to theprocessor, wherein the processor executes instructions to determine thelocation of the virtual probe tip, the instructions comprising a set ofcorrelation factors that are utilized to correct the location of thevirtual probe tip to account for the flexing of the portion of the probeout of the predetermined alignment; forming a sonogram of the subdermalsite on a monitor from information communicated to the processor fromthe ultrasound transducer; and forming an image on the sonogram of thelocation of the virtual probe tip as determined and correlated by theprocessor from information communicated to the processor from thedetector.
 2. The method according to claim 1, wherein the instructionsexecuted by the processor include the solution to the equation:S ₀ =S _(H)+(a*H+c)*L _(B) +b*H+d wherein L_(B)—the portion of the probeas measured from the second end of the probe guide to the target S₀—thelocation of the target as would be determined by the detector when theprobe remains in the probe path that includes the predeterminedalignment S_(H)—the location of the target as determined by the detectorfollowing the flexing of the portion of the probe out of thepredetermined alignment H—A level index that represents the number oflevels out of the predetermined alignment that the portion of the probeis flexed a, b, c, d—correlation factors for the ultrasound device. 3.The method according to claim 2, wherein the correlation factors are:a—between about −0.045 and about −0.055, for instance about −0.050;b—between about 4 and about 5, for instance about 4.3; c—between about0.02 and about 0.03, for instance about 0.028; d—between about −0.5 andabout −0.06, for instance about −0.053.
 4. The method according to claim2, wherein the correlation factor a is about −0.050, the correlationfactor b is about 4.3, the correlation factor c is about 0.028, and thecorrelation factor d is about −0.053.
 5. The method according to claim1, wherein the detector comprises an array of sensors.
 6. The methodaccording to claim 5, wherein the sensors are Hall effect transducersand the target is a magnet.
 7. The method according to claim 5, furthercomprising grouping the sensors and providing their outputs to a seriesof multiplexers.
 8. The method according to claim 7, further comprisinganalyzing the output of a group of sensors, a center sensor of the groupregistering the highest or lowest voltage output of the group.
 9. Themethod according to claim 5, further comprising developing a vector setof values corresponding to a predetermined signal and comparing thatvector set to a vector set as determined by the sensor array.
 10. Themethod according to claim 1, wherein the image of the location of thevirtual probe tip comprises an image of a virtual subdermal portion ofthe probe.
 11. The method according to claim 1, further comprisingconfiguring the processor to determine an index level corresponding tothe flexing of the portion of the probe out of the predeterminedalignment and an associated movement of the target in relation to thedetector.
 12. The method according to claim 11, wherein the processorinstructions comprise the triggering of an alarm when the index levelexceeds a predetermined value.
 13. The method according to claim 1,further comprising determining one or more offset values for theultrasound device and incorporating the offset values in the processorinstructions.
 14. An ultrasound device comprising: an ultrasoundtransducer for emitting and receiving sonic waves; a probe guide forguiding a probe, the probe terminating at a probe tip, the path of aprobe guided through the probe guide defining a known correlation withsonic waves emitted by the ultrasound transducer, the probe guideincluding a first end and a second end, the second end being fartherfrom a skin contacting surface of the ultrasound device than the firstend; a detector for detecting the location of a target associated with aprobe that is guided through the probe guide, the path of the probeguided through the probe guide including a predetermined alignmentbetween the target and the detector; a processor in communication withthe ultrasound transducer and with the detector, the processor beingconfigured to execute a set of instructions to determine the location ofa virtual probe tip, the instructions comprising a set of correlationfactors that are utilized to correct the location of the virtual probetip to account for flexing of a portion of the probe out of thepredetermined alignment as the probe is guided through the probe guide.15. The ultrasound device according to claim 14, wherein the detector isan array of sensors.
 16. The ultrasound device according to claim 15,wherein the sensors are Hall effect transducers that are sensitive to amagnetic field.
 17. The ultrasound device according to claim 15, whereinthe array is a linear array.
 18. The ultrasound device according toclaim 15, wherein the array comprises sensors that are canted at anangle and are provided in multiple rows with the sensors staggeredrelative to one another.
 19. The ultrasound device according to claim14, wherein the instructions executed by the processor include thesolution to the equation:S ₀ =S _(H)+(a*H+c)*L _(B) +b*H+d wherein L_(B)—the portion of the probeas measured from the second end of the probe guide to the target S₀—thelocation of the target as would be determined by the detector when theprobe remains in the probe path that includes the predeterminedalignment S_(H)—the location of the target as determined by the detectorwhen a portion of the probe is flexed out of the predetermined alignmentH—A level index that represents a number of levels out of thepredetermined alignment that the portion of the probe is flexed a, b, c,d—correlation factors for the ultrasound device.
 20. The ultrasounddevice according to claim 19, wherein the correlation factors are:a—between about −0.045 and about −0.055, for instance about −0.050;b—between about 4 and about 5, for instance about 4.3; c—between about0.02 and about 0.03, for instance about 0.028; d—between about −0.5 andabout −0.06, for instance about −0.053.
 21. The ultrasound deviceaccording to claim 19, wherein the correlation factor a is about −0.050,the correlation factor b is about 4.3, the correlation factor c is about0.028, and the correlation factor d is about −0.053.
 22. The ultrasounddevice according to claim 14, further comprising an alarm, wherein theprocessor is configured to determine an index level corresponding to theflexing of the portion of the probe out of the predetermined alignmentand an associated movement of the target in relation to the detector,the processor instructions comprising the triggering of the alarm whenthe index level exceeds a predetermined value.
 23. The ultrasound deviceaccording to claim 14, further comprising a sterilizable shield thatencloses at least a portion of the ultrasound device.
 24. The ultrasounddevice according to claim 14, further comprising a clamp for clamping aprobe within the probe guide.
 25. The ultrasound device according toclaim 14, wherein the predetermined alignment is parallel to thedetector.
 26. The ultrasound device according to claim 14, wherein theultrasound device includes multiple removably attachable portions, afirst portion defining the probe guide and a second portion includingthe ultrasound transducer.